This project aims at purification and characterization of Seminal Plasma Immune Response Inhibition, studies on the site of its synthesis in the male reproductive tract, cellular and molecular mechanisms involved in the inhibiton of immune response and finally the role of the inhibitor in the etiology of immune-fertility. In the first ten months, progress was made on purifying a component which efficiently suppressed ConA and allogenic induced responses (human T lymphocytes) using Sephacryl S-300 and Sephadex G-100 chromatography. The purified preparation was extensively checked for lack of non-specific lymphocytotoxicity activity using cell survival assays for five days and typan blue exclusion assays. Fractions prepared by isoelectrofocussing and by other purification procedures were prepared for testing in the in vitro lymphocyte culture system.